1. Field of the Invention
The present invention relates in general to a blood-pressure measurement apparatus capable of heart function assessment.
2. Related Art Statement
In order to diagnose a state of circulating system, a blood pressure is conventionally measured. Although a heart is one of circulatory organs, it is difficult to assess a heart function, only by measuring the blood pressure. Sometimes it is needed to assess the heart function as well as the blood pressure.
In order to assess a heart function of a living subject, such heart function parameters are calculated as an ejection time, which is an actual period of ejecting blood from the heart, a pre-ejection period, which is a period from a start of cardiac muscle activity to actual starting of blood ejection, and a cardiac mechanical efficiency. These parameters can also be calculated based on a waveform of an aorta pressure-pulse. For example, the ejection time can be calculated based on a period from a rising point of an aorta pressure-pulse-waveform to a dicrotic notch of the same. Also, the pre-ejection period can be calculated based on a period from a Q-wave appearing point of an electrocardiogram to the rising point of the aorta pressure-pulse-waveform.
However, since the aorta pressure-pulse-waveform is difficult to be detected non-invasively, apparatus for assessing the heart function have been proposed, wherein the aorta pressure-pulse-waveform is estimated from an arterial pressure-pulse-waveform measured at another position in the living subject, and the heart function parameters are calculated. For example, apparatus in JP-A-11-113860, JP-A-2000-333910 and JP-A-2000-333911, which have been filed by the present applicant and laid open in public, are such apparatus. According to the apparatus in the Publications, an aorta pressure-pulse-waveform is estimated based on a radial artery pressure-pulse-waveform detected at a wrist and then, based on the estimated aorta pressure-pulse-waveform, heart function parameters are calculated. Also, at the apparatus, blood pressure can be measured as well as heart function parameters.
However, as for the apparatus noted in the applications, it is needed to adapt an inflatable cuff to be wrapped around an upper-arm portion, to put a radial pressure-pulse-wave detecting probe, internally containing a pressure-pulse-wave sensor, on the wrist, to stick a plurality of detecting electrodes of electrocardiograph on predetermined points of living subject, and further to place a heart-sound microphone in the vicinity of a heart. It is considerably cumbersome to put on these devices. Therefore, such apparatus is desirable that can more easily assess heart function as well as can measure a blood pressure. Especially, for the recent growing importance of medical care at home, such apparatus is desirable that can readily measure heart function as well as a blood pressure at home.
It is therefore an object the present invention to provide a blood-pressure measurement apparatus capable of heart function assessment, which is easy to put on.
After extensive studies to achieve the object, the present inventor discovered following fact that is, when a blood-flow in an artery of an upper-arm portion is stopped with such cuff as used for blood pressure measurement, a pressure-pulse waveform, detected at an upper stream side of the blood-flow stopped position, is the same waveform as an aorta pressure-pulse-waveform, therefore, if a pressure-pulse wave sensor is combined with the cuff, and if pressure-pulse-wave sensor is used to detect the pressure-pulse waveform while the blood-flow in the upper-arm portion is stopped with the cuff, it is possible to put on the cuff for blood pressure measurement and, at the same time, the sensor for detecting the aorta pressure-pulse-waveform. This invention is developed based on this fact.
According to the first invention, there is provided a blood-pressure measurement apparatus comprising (a) a variable pressure and blood-flow stopping cuff to be wrapped around an upper-arm portion of a living subject, that measures a blood pressure of the living subject by changing a pressing pressure of the cuff according to a predetermined speed, the apparatus comprising a blood-flow-stopping means for stopping blood-flow at the upper-arm portion with the cuff, (b) a pressure-pulse wave sensor equipped being combined with the cuff so as to detect a pressure-pulse-wave, appearing at an upper-stream side of the blood-flow stopped position and, (c) a heart function parameter calculating means for calculating a heart function parameter of the living subject, based on the detected pressure-pulse wave at the upper-stream with the sensor, while the cuff is stopping the blood-flow in an artery of the upper-arm portion.
According to the first invention, since the pressure-pulse wave sensor detects upper-stream than the blood-flow stopped position by the cuff, a pressure-pulse waveform, which is detected with the pressure-pulse wave sensor while the cuff stops the blood-flow in the artery of upper-arm portion by blood-flow stopping means, is the same waveform as an aorta-waveform. Therefore, the heart function parameter can be calculated with a heart function parameter calculating means based on the pressure-pulse wave detected with the sensor. Also, a blood pressure can be measured with the same cuff that is wrapped around the upper-arm portion. As a result, decreased number of devices to be put on the living subject leads to readily putting-on for the measuring the heart function parameter and a blood pressure.
The second invention in order to achieve the object is that the heart function parameter calculating means calculates an ejection time ET from a time of a pressure-pulse wave rising-point to a dicrotic notch of the pressure-pulse wave of the upper-stream detected by the pressure-pulse wave sensor.
According to the second invention, the ejection time ET can be calculated only from the pressure-pulse-wave, which is detected by the pressure-pulse wave sensor, which is combined with the cuff, and any other sensor is not needed to be put on to detect other signals of the living subject than pressure-pulse wave sensor. So it leads to easy device putting-on for heart function parameter measurement.
According to the third invention in order to achieve the object, the apparatus according to the first or second invention further comprises (a) a plurality of electrodes to be adapted to stick on predetermined positions of the living subject, and (b) an electrocardiograph to detect, via the electrodes, an electro-cardiac signal representing activity-potential of cardiac muscle, wherein the heart-function parameter calculating means calculates a pre-ejection period PEP, as a time difference, that is, a period of time, from Q-wave detected time of the electro-cardiac signal, which is detected via the electrodes by the electrocardiograph, to the time of the rising-point of pressure-pulse-wave, which is detected by the pressure-pulse wave sensor.
As for the apparatus according to the filed patent application JP-A-11-113860, in order to measure an ejection time, a cuff, pressure-pulse wave sensor and a heart-sound microphone are needed to be put on the living subject and, in order to measure a pre-ejection period of time, a plurality of electrodes, equipped with the electro-cardiograph, in addition, have to be put on the living subject. On the other hand, according to the present invention, in order to measure the ejection time and the pre-ejection period, all the devices that have to be put on the living subject are the cuff and a plurality number of electrodes.
According to the fourth invention in order to achieve the object, the heart function calculating means calculates a cardiac mechanical efficiency, which is one of heart function parameters, as a ratio of an aorta effective elastance Ea to a left ventricle tele-systolic elalastance, based on a ratio of the pre-ejection period PEP to the ejection time ET.
According to the fifth invention, the apparatus comprises a plurality number of the pressure-pulse-wave sensors, which are arranged in a lengthwise direction at an inner peripheral face of the cuff so as to assure sufficient sensitivity.
According to the sixth invention, the pressure-pulse-wave sensor comprises a plurality number of pressure-sensitive semiconductor elements, which are arranged in a lengthwise direction at a pressing face of the pressure-pulse-wave sensor. And the apparatus of the first invention further comprises an optimum detective element determining means for selecting a most appropriate element from a plurality number of pressure-sensitive semiconductor elements.
According to the present invention, it is preferable that the blood-flow stopping means should be such, that a pressing pressure of cuff is increased at a predetermined quick speed to reach a predetermined blood-flow stopping pressure, which is a sufficient pressure to stop a blood flow in the artery of the upper-arm portion, and thereafter, is maintained for predetermined period of time and then, the cuff pressure is decreased at a predetermined slow speed. Thus, while the cuff pressure is maintained at the blood-flow stopping pressure, heart function parameters can be calculated, and also in the course of slowly decreasing cuff pressure, the blood pressure measurement can be performed. Therefore, by increasing a cuff pressure only one time, both blood pressure and heart function parameters can be calculated.